It is well known that water effectively suppresses or “puts out” a flame by lowering the flame temperature and reducing the concentration of oxygen available for the combustion process. For example, water mists have met with recent success as a fire suppression agent. The temperature of the flame is lowered because the high latent heat of vaporization of water absorbs energy from the flame as the water evaporates. The concentration of oxygen is lowered because the water droplets actually displace oxygen as they evaporate.
One of the drawbacks of employing water mists is the difficulty in producing such mists in confined areas and the fact that water can evaporate before it reaches the base of the flame. Halons have been used to overcome these types of problems; however, they contribute to global warming and ozone depletion. Furthermore, production of halons is currently banned by international agreement. Conventional halon replacements have been found to be either ineffective and may contribute to global warming and/or ozone depletion.
There is a current need for a water droplet system that can effectively deliver water droplets to the flame, extract sufficient energy from the flame by evaporation of the water droplets, displace oxygen with the vaporized water, and inhibit the flame propagation reaction.
When halon production was barred in the early 90's due to its strong contribution to ozone depletion and global warming, an intensified effort was begun to find suitable replacement agents. Because the agent should be adaptable for indoor use, it was necessary to find non-toxic agents. In addition, because of the need to suppress fires that may endanger and even engulf electronic components, it was necessary for the agent to be gaseous or liquid with low residue.
After considering a variety of materials, small particle water mist (from 10-100μ in size) was found to meet many of the requirements of a successful flame suppression agent. For example, advantages to the chemical nature of water include the following:                1. Evaporation of water produces water vapor that acts as an inert gas to reduce the concentration of oxygen.        2. Water is non-toxic.        3. Water does not contribute to ozone depletion.        4. Vaporization of water is very endothermic due to the large enthalpy of vaporization, which lowers the flame temperature.        5. Water does not contribute to global warming.        
However, water droplets have several problems that must be overcome before they can be utilized in flame suppression. These problems include:                1. Water freezes below 0° C.        2. Distribution of small size water droplets is difficult.        3. Production of monodispersed droplets is very difficult.        4. Projection of water mist into a fire is difficult.        5. A large portion of the water droplets evaporate before they reach the flame.        
As will become clear from the following, the present invention provides a way of realizing the benefits from using small size water droplets, or water-containing droplets, to retard and suppress a flame while, at the same time, overcoming the known problems associated with the use of such water droplets.